Electrolytic cleaning and pickling of metal surfaces



March 27, 1945. J NACHTMAN 2,372,599

ELECTROLYTIC CLEANING AND PICKLING OF METAL SURFACES Filed March 29,1940 Patented Mar. 27, 1945 ELECTROLYTIC CLEANING AND PICKLING OF METALSURFACES John 8. Nachtman, Pittsburgh, Pa.

Application March 29, 1940, Serial No. 328,632

6 Claims.

This invention relates to the cleaning of metal surfaces; it involvesthe washing of the metal surface with liquid, ordinarily water or anaqueous solution; and consists in the establishment of conditions ofelectrolysis, under which the washing proceeds. In the electrolyticarrangement the water-flooded sheet may be the cathode, it may be theanode, or, though neither cathode nor anode, it may yet be immersed inthe electrolyte, and in either case the effect of electrolytic actionwill be to render the cleaning process more effective. The inventionfinds practical application in the cleaning of steel strip, and in thatapplication I shall describe it.

In the accompanying drawing Fig. I is a diagrammatic view in verticaland longitudinal section of apparatus for cleaning'steel strip, in theoperation of which this invention may be practised. Figs. 11 and III arelike views of other cleaning apparatus: Fig. II, specifically, ofpickling apparatus; Fig. III of electro-plating apparatus. Fig. IV is anenlarged diagrammatic view showing the electrical connections toone ofthe sprays and to one of the brushes.

Referring to Fig. I, the apparatus there shown is designed and intendedfor the removal of grease from the surface of the strip. It consists ofhot-water scrubber A, drier B, cleaner C, hotwater rinse D, and drier E.These several pieces of apparatus are arranged in succession, end toend, and the strip 8 to be cleaned advances through them from left toright, in continuous course.

The hot-water scrubber A is provided to remove the heavier part of thecoating of grease, oil, and dirt that fouls the strip. It consists of atank I, provided with a hood 2 and an exhaust 3. Exhaust 3 may beunderstood to be connected to an exhaust system, not shown. Withintank'i are mounted rotating metallic brushes 4 (preferably of stainlesssteel and driven by individual motors), backing-up rolls 5, hot-watersprays i (100 pounds pressure at 180-210 R), and squeegee rolls I. Thebrushes 4 are preferably provided, as here shown, in plurality (thenumber will depend upon the speed of the strip), and arranged to engagesuccessively both surfaces of the advancing strip; the backing-up rolls5 are severally paired, each with a brush 3, and are adapted to sustainthe strip while the brush scours its opposite surface; the hot-watersprays also plays upon both surfaces of the strip. The Jets from thesprays may be directed obliquely to the surface of the strip, andsuccessive jets may be oppositely inclined, as the drawing hows. The

squeegee rolls are paired and set to engage simulas it advances betweenthem. Brushes l are rotated to give a speed of approximately 3000 f. p.m. brushing speed on the strip, and they are preferably rotated in adirection contrary to the advance of the strip. Backing-up rolls 5 andsqueegee rolls 1 are driven at strip speed, and in the direction ofstrip progress. Sprays 6 receive hot water under pressure fromcompartment 33 (presently to be described) through a pipe connection 39.The waste water from tank I with its burden of fouling material iscarried to the sewer by drain-pipe 8.

In case the sewer capacity is not sufllcient to take care of the greaseand oil removed in the scrubber A, they may be separated out in asettling tank, as shown. The discharge from pipe 8 is secured in a tank50. It is essentially a mixture of grease and water. Due to the lowvelocity of the oily mixture through the tank, the oil and grease willrise to the surface and pass over partition 51, and escape throughpassageway 53 to a place suitable for disposal. The water collecting intank passes beneath bafiie 53 to compartment Ill, and then overpartition 58, through passageway I2 to the sewer.

The splash from the brushes 4 is caught by baifles 20 and 2| anddirected to tank I, thereby leaving the strip relatively dry when itenters the squeegee l. The squeegee I attenuates the water film upon thestrip, so that it can be quickly dried in the drier B. This feature willbe the better understood when it is remembered that the strip is stillcoated with an oil fllm, and. water willnot adhere to its surface.

The drier B consists of tank 9, hood l0, and exhaust ll, heated rollsl2, and a hot-air supply (not shown) for circulating hot air around theheated rolls I2. The purpose of this drier is, by removal of water fromthe strip, to prevent dilution of the cleaning solution in the tank l3.Rolls I2 are provided in pairs; there is advantageously a plurality ofpairs of them; they engage the strip advancing between them; they aredriven in the direction of strip progress, and preferably at stripspeed; and may be heated in convenient manner, as by gas, steam, orelectricity.

The mechanical cleaner, water rinse, and solutron-recovery system C, Dis an integral unit and includes a tank l3 with hood l4 and exhaust i5.Tank I3 is divided into two compartments 2'! and 33, by partition 22.Concentrated cleaning solution is maintained in compartment 21, whilethe concentration in compartment 33 will be very much less, as will bemade plain in the following description. Within tank i3 are mountedrotating metallic wire brushes it, Hi, and I8, with backing-up rollsiii. As shown, the axes of rotation of these brushes are in planesparallel to the strip so that the brushes brush the strip tangentially.These brushes are preferably of stainless steel and are driven byindividual motors to give a brushing speed of approximately 3000 f. p.m. rotating against the travel of the strip. The backing-up rolls aredriven at strip-speed and in the direction of strip advance. Theorganization is that already described, of the brushes 4 and theirbacking-up rolls 5, in scrubher A.

Concentrated cleaning solution, essentially alkaline, maintained incompartment 21, is kept constantly in circulation. It is withdrawnthrough drain 28 and is pumped by pump 29 through filter 30, heater 3|,and pipe 32 back to sprays 23. The sprays 23 (of greater number) arearranged toward the intake end of the cleaner C, while other sprays 24(less in number), presently to be described, are arranged toward thedelivery end. All the sprays are advantageously arranged to delivertheir jets obliquely upon the surfaces of the strip, and successivesprays may deliver oppositely directed jets. The sprays deliver theirjets from above and below upon the strip as it advances, and thesolution collects in compartment 21. The strip advances in horizontalcourse, at higher level than the surface of the pool of solution incompartment 27. The discharge from sprays 23 is in continuous stream ata pressure of l to pounds. The pressure is as high as is permissiblewithout undue foaming.

Bafiies and 2|, similar to those already described, catch the splashfrom the brushes and direct the solution back to the pool in compartment2] for recirculating and reheating.

The sprays 24, arranged toward the delivery end of cleaner C, receivethrough pipe 38 and from a source presently to be described, hot waterunder pressure in quantity sufficient to make up for dragout andevaporation, and to maintain the level of the pool of cleaning solutionin compartment 21. The amount of water so supplied under pressure tosprays 24 is controlled by float valve 38A. The sprays 24 deliver hotwater on the strip in a high-pressure atomized spray that dilutes thesolution. of the film upon the strip. This diluted film is picked up byother brushes I! and thrown against other baflies 20 and 2| and divertedback to pool-compartment 21.

Yet other sprays 25, arranged adjacent the path of progress of thestrip, beyond the partition 22 that defines the compartment 21, andwithin the portion of the apparatus indicated by the letter D and termedthe rinse, receive hot water under high pressure from pipe 57?. Jetsfrom sprays 25 directed both rearwardly and forwardly, as shown,impinging upon the strip from above and from below, thoroughly wash thestrip, and, in cooperation with the scrubbing action of brushes l8,remove all cleaning solution from the strip and replace the film ofsolution upon the strip with a film of water. The water collecting incompartment 33 is recirculated by mentioned brushes l8 and direct thewater back to compartment 33 without rewetting the strip.

The sprays 25 are arranged toward the intake end of rinse D. Othersprays 23, less in number than sprays 25, are arranged within the rinseto ward the delivery end. Sprays 26 are supplied with fresh, hot waterunder pressure from a source not shown, and deliver jets of fresh, hotwater under pressure upon the strip to rinse it completely. The rinsewater is largelyremoved by the squeegee rolls 41. The rinse watergathers in a pool or compartment 33 and excess is discharged through anoverflow pipe 40,

The drier E is similar to B, and consists of tank 4|, heated rolls 44,hood 42, and stack 43. The strip at this point, free of oil, is filmedover with water, and is on that account more diflicult to drycompletely. The drier E may, therefore, be desirably of larger capacitythan drier B,

In size the units are suited severally to the speed of operation and thenature of the steel that is being cleaned. In some cases it may bedesirable to omit units A and B. In the case of strip stock that hasbeen annealed; or, again, in the case of skin-rolled dry or hot-rolledstock that has been flattened or annealed; the surface does not carryheavy grease. It is in such cases as these that scrubber and drier maybe omitted. In other cases, as, for example, when the strip is beingprepared for electro-plating, the strip is kept wet, to prevent thefilmin over of the cleaned surface; and the wet strip is advanceddirectly into the electro-plating bath. In such case the drier E will beomitted.

It is to apparatus so constructed and organized that my invention may beadded, and the method of cleaning that is accomplished in the operationof that apparatus, carried out under the conditions of my invention,will be found to be in greater degree efficacious.

I provide a low-voltage generator. The sprays will be understood to bemetallic (and, accordingly, electrically conducting) nozzles thatdeliver jets of liquid (also electrically conducting) upon the surfaceof the strip (which also is electrically conducting). I preferablyconnect one terminal of the generator G to the sprays 23, and the otherterminal to the rotating brushes I6. I obtain fastest cleaning when Iconnect the positive terminal to the sprays 23 and the negative terminalto the'brushes It? as shown in Fig. IV. I preferably employ a currentdensity of 3000 to 5000 amperes per square foot of jet crosssection.Under these conditions there is a rapid evolution of hydrogen on thestrip where the spray strikes the strip, and a rapid evolution of bothhydrogen and oxygen adjacent the portion of strip that is being brushed,with result that the film of oil is removed almost instantly and isturned to soap by the cleaning solution.

As shown in Fig. IV, the shaft of each rotating brush it may have acurrent collecting drum 20 at one end with a contact brush 205 slidablycontacting the same for conducting current from a generator G to thebrush.

The electrolytic condition may be imposed upon the cleaning operation byother arrangements of the current connections, but such otherarrangements will, however, be less eilective in producing anelectrocleaning action. For example, half of the sprays 23 may beconnected with the positive terminal of the generator, and the otherhalf withthe negative terminal; or, again, the backing-up rolls itwithin the extent of the compartment 2'! may be connected with oneterminal and either the Jets at: the cooperating th n It with theotherterminal. In some-cases it will be desirable'to electrify'themetallic brushes-f" 4 in' the scrubber A by connecting them to one orthe other terminal of the generator. Half of the brushes [6. may, forexample, be connected to the positive terminal of the generator and halfto the negative terminal; and other such permutations may be made.

Alternating current maybe used, or alternataavaaao V cold water at highpressure from nozzles l and to .the flexingfaction of passing betweenrolls, II,

which are adjustable m ne vertical direction and are driven at stripspeed. The leng'thof unit F is sufficient to reduce the temperature ofthe strip to approximately 200 F. The strip then advances ,through thescale breaker-G, \vhere'it is bent back; d forth to loosen the adheringscale.

ing current maybe superposed on direct cur-'- H characteristic is therapid "evodrogen gas, generated at the surface of the strip, f I

it will be effective-not only in aiding the mechanicalremoval-of'material that fouls the surface; it will tend also to reducedoxide that may be rolled into, the surface and in that resp t also toimprove the surface. 7

The cleaning apparatus that is shown in Fig. 11 is, specifically,apparatus for the pickling of metallic strip, and like the cleaningapparatus of Fig. Lit is designed for. operation upon strip as itadvances in continuous course. In the operation of this apparatus ofFig. II also the invention may be practised. The apparatus consists of acold-water spray F,'a scale breaker G, a scrubber H, aipickler I,a-rinse-J. and a drier K. These pieces of apparatus are organized tostand in successive position's, that the strips of material moving fromleft to right may progress in continuous course through them. Thepickling apparatus willbe described for the pickling of strip steel.

In the present methodsof manufacture ofstrip steel the steel ishot'rolled to a thickness of approximately 0.070 to 0.125", and is thencoiled before being further processed. During the hot rolling andcooling a heavy scale of iron oxide From e scale breaker the stripadvances to the scrubber K. As the strip enters, H it is floodedwithacid pickling solution from nozzles 62 and .is'scrubbed by rotatingmetallic wire brushes 03 against backing uprolls 04. Rolls 64 are drivenatystrip speed, and brushes 63 are driven to give .abrushing speed ofapproximately 3000 f. p. m.

whilerotating in the same direction with that of strip travel... (Whenthe material under treatment is in the form of discontinuous sheets, the

control will'be so arranged as to stop the brushes as the-end of thesheet is approached.) The brushes .perform two mechanical-functions:first,

they removescale; and, second, they remove the spent acid, so'that'fresh acid-from succeeding sprays 82 may come into immediatecontact with v a chimney 69, and the enclosed apparatus. The

strip advances in horizontal course through the tank and at higher levelthan the surface of the pool of pickling solution that collected in thetank--all as indicated in the drawing.

When the strip has left scrubber H and entered pickle!" I, it is sprayedwith electrified-acid sprays 66 and flexed back and forth by rolls I0which are driven at strip speed. Thespray nozforms upon the surface;and, before the strip can passed through pickling apparatus thatincludes a long tank of acid solution, in which the strip is submergedfor several minutes. Because of the length of the tank, the tension uponthe strip is necessarily very high, and the machinery must be quitemassive. In the practice of the present invention the scale may beremoved much more rapidly and in such a manner that the strip need beunder no tension and the machinery may be relatively light. Theapparatus here shown is designed with the expectation that it willreceive the strip directly after the hot rolling and while the strip isstill in the form of a long flat sheet; but I desire to make the factplain that the apparatus may be associated with uncoilers and othernecessary mechanism for straightening out a coil of strip and forfeeding it into this pickling machine. In such case, as will beunderstood, the invention will be practised upon strip that has beencoiled after passing through the hot rolling mill.

From the hot mill (in preferred procedure) the strip is run out On acooling table and cooled to a temperature that will permit the strip tobe sprayed with water. The leading end of the strip is then caused toadvance first throug unit F. Unit F consists of a suitable chambe withinwhich the advancing strip is subject to sprays of zles 66 are preferablyconnected to the positive terminal of an electric generator and eitherthe rotating brushes 'H or the rotating brushes G3 in the scrubber H orboth may be connected to the negative terminal; and a current ofapproximately 3000 amperes per square foot of spray cross-section iscaused to flow. Under such conditions the strip becomes the cathode ofan electrolytic cell and hydrogen gas is generated at its surface.

In some cases it may be advisable to connect also the acid sprays 62within the scrubber H to the positive terminal of the generator, so thathydrogen gas forms on the surface of the strip while scale is beingremoved by the brushes 63. Such an enlargement of the number of thesprays that are electrified results in more rapid pickling.

As in the case of the cleaning procedure described with reference toFig. I, other arrangement of current connections are permissible thoughI have described that which I believe to be best. For example, half ofthe sprays 66 may be connected to the positive terminal of the generatorand the other half to the negative terminal; the sprays 82 may beconnected to one terminal and the sprays G6 to the other; and otherarrangements are permissibleit being requisite only that gas be evolvedelectrolytically at the strip surface, in the area being sprayed upon orscrubbed.

I have found that alternating current, or alternating currentsuperimposed upon direct current, is eiIective in accelerating the speedof pickling.

The solution ordinarily will be acidic; but other chemically efl'ectivecleaning operations, using solutions that are non-acidic, are known tothe metal-cleaning industry; and, manifestly, the invention heredescribed is of general applicability, and is not conditioned by norlimited to association with an acidic solution.

Pickling solution is supplied under pressure to sprays 62 and 66 throughpipe 12. The solution caught in tank 61 is withdrawn, as in theapparatus of Fig. I already described, and is circulated by pump 13through filter l4 and heater to pipe 12, and thence back to the sprays.Recirculated water, through pipe 18, is sprayed on the strip by sprays11 that are situated within the pickler I toward the delivery end. Theydirect their jets upon the strip after it has passed beneath the sprays68. These water sprays 1T dilute the acid film on the strip before it isacted upon by brushes ll. These brushes engage, one the upper, the otherthe nether, surface of the strip before the strip passes from thepickler I, and the strip when it is made subject to the action of thesuccessive brushes is backed by a cooperating roll 93. Baflles 95 and 96catch the splash from brushes II and return it to tank 61.

The amount of water supplied to sprays I1 is controlled by a float valveI8 to make up for evaporation and dragout. The temperature of thepickling solution should be maintained at approximately 120 to 180 F.The density of cur-- rent applied to sprays 66 and 62 should varyinversely with the temperature.

The rinse J consists of a tank M, a hood 82, a chimney $3, and theenclosed apparatus. The strip enters it from the pickler I and advancesthrough it in horizontal course and at a higher level than the surfaceof the pool of water that collects in the tank-all as indicated in thedraw- In rinse J the strip is washed by water delivered through spraysI9 and scrubbed by rotating metallic wire brushes 80 (with cooperatingbacking rolls 94) to remove all traces of acid and metallic salts fromthe strip. Fresh hot water from a source not shown is supplied to sprays04 that are arranged toward the delivery end of the rinser, and in anamount to keep the contents of the tank 8| sufficiently diluted. Aconstant level is maintained in tank 8| by an overflow pipe 85, throughwhich the excess is passed to the sewer. From the pool in tank BI wateris drawn through a pipe 86 and driven by a pump Bl through a filter 80and a heater 09, and is delivered through two leads: through lead I6(which as has been explained is valve controlled) to the sprays ll inthe pickler I, and through the lead at to sprays 19 in the rinse J. ofthese two sets of sprays the set I9 delivers its jets first upon theadvancing strip, and afterward the set 8%. Bailles s1 and 98 catch thesplash from brushes 80 and return it to tank 8| Squeegee rolls 9| at thedelivery end of the rinse attenuate the water film on the strip, so thatit can be quickly removedby the heated rolls er in drier K. The strip asit emerges from drier K is oiled and coiled in the usual manner andstored for further processing.

If the strip to be pickled is cold (as it would be if taken from storagein a coiled form) the high-pressure water sprays 6| will not be employedand heated rolls will be used in place of rolls SI, to bring the stripto the approximate temperature of 200 F.

Strip pickled in the manner described is in better condition for furtherprocessing than strip pickled the old way, because it is free of foreignmatter such as carbon, smudge, etc., and is in ideal condition for coldreducing or for coating ing or cracking of the coating.

with a protective coating-as by electroplatin hot dipping with zinc,etc.

A distinct advantage of the pickling operation, carried out with theemployment of my invention as described, is that most of the scale,mechanically removed from the strip. will be carried by the circulatingstream of the pickling solution to theillter. It will there beseparated, so that the solution will not continue to react with it; and,in consequence, the life of the solution for its intended useful purposewill be prolonged.

A third case, illustrative of the practice of my invention, is the caseof the hot-dip coating of steel strip-as, for example, galvanizing. Inslowspeed continuous hot-dip coating, the strip is advanced successivelythrough a fiuxing tank and a hot-coating tank. The invention ispracticed by arranging in the line of advance of the strip as itapproaches the fiuxing tank such a unit as that indicated at A, Fig. I.The solution used in the sprays 6 may be acid, alkaline, or neutral,depending on the type of flux used and on the condition of the surfaceas it comes to be treated. The electrolytic evolution of gas at thesurface of the strip advancing through the unit A may be brought aboutby connections such as those already specified. Within the unit A, inthe manner already described, the strip is prepared for fluxing. It isimportant that the surface cleaned in unit A be not permitted to drybetween the cleaning and the fluxing steps of the operation. As long asthe surface is kept wet, no superficial film will form to interfere withfluxing. Tests show that, when the surface of the strip has beenprepared in the manner indicated, a higher quality is achieved in thecoated plate. The coating will be more uniform and more closelyadherent. In consequence, deeper drawing of the coated strip becomespossible without peel- Incidentally. speed of operation may beincreased.

The use of rotating brushes of stainless steel wire has peculiar valuein this association. Coldrolled strip carries rolled into its surface(as elsewhere herein explained) the products of oil broken down by heat.Cleaning mechanism in common use in this association leaves the surfaceinadequately cleaned and the consequence is a product whose qualityadmits of improvement. I find that with the scrubbing mechanism of unitA arranged as last described, and particularly by virtue of thescrubbing effect of brushes of stainless-steel wire, the strip goes tothe fiuxing bath in singularly clean condition, and, in consequence, thequality of the product is improved. The invention described inassociation with galvanizing procedure is applicable generally tohot-dipping procedures, as in the making of tin-plate and terne-plate.

The invention may be practised in association with the electro-platingof sheet; and when so associated, the cleaning current and the platingcurrent may be derived from a common source. This is illustrated in Fig.III. In this figure a strip S that may be understood to be a strip ofsteel advances in continuous course through a plating bath within atank. Anodes IOI are arranged within the bath in suitable position withrelation to the advancing strip. The strip itself becomes the cathode.The electro-plating circuit may be completed through the brushes I02that scour the sheet as it advances to the tank I00; and if, in themanner already described, the sprays I03 that direct their jets upon thesheet as it approaches the scouring brushes I02 be conasvasoe r nectedwith the positive terminal of the source of electric energy (with whichterminal the anodes iii also within the electro-plating tank areconnected), it is manifest that from the same source of energy may bederived both the gas-generating current that aids in cleaning the stripand the electro-plating current that efl'ects the deposit of metal uponthe strip. In some cases it will be desirable to connect the anodes tothe positive terminal of a voltage source different from that whichsupplies the current for the sprays I03, in order that the two currents,

for plating and for cleanin may be independently adjusted. The contactthrough which the strip is brought intocircuit may be through thebrushes I02 or through the backing-up rolls I, or through both.

In the bluing of strip, as distinguished from electro-plating, the stripmay be made the anode in an electrolytic bath, and in such case theposiratus of Fig. I, the pickling operationperfonned by the apparatus ofFig. II, the dipping operation, and the plating and bluing operationslast describedsuperficial fouling material is removed from the surfaceof the metal. In one case this fouling material is grease, in another itis scale, in yet another it is rolled in hydrocarbon pollution. In eachcase the cleaning operation inremaining on the strip-ma in the ensuingrolling operation be rolled into the surface, and in such cases as thesethe invention is effective, to

afford more adequateand complete removal of .the surface-foulingmaterial.

I have found by actual test that brushes formed of stainless-steel wirewill be effective, under the conditions brought about in the practice ofthe invention described, to remove most films that under prevalentrolling-mill practice are rolled into strip'surfaces. This is due to thehigh tensile strength, the elasticity, and the non-corrosive characterof stainless steel.

In all operations such as those described, where strip is beingpropelled at high speed and liquid is in contactwith the surface of thestrip, the liquid is set in motion and carried along with the strip;and, unless preventive means be prof vided, the dragout of the liquid(which ordinarily is a solution of some relatively costly salt) resultsin a loss that may be such that in particular cases operation ceases tobe profitable. Indeed, in conventional cleaning operations, this dragoutof cleaning solution is the major item of expense. With this observationin mind, it will be remarked of the apparatus that has been describedthat in each case rotating wire brushes are set toward the delivery endof the tank, and that the strip as it approaches these brushes issprayed upon with limited quantities of water; and baffle plates areadded, against which the brush-thrown solution impinges, and by whichvolves the flushing of the fouled surface with liquid, and,specifically, aqueous liquid-acid. alkaline, or neutral. The inventionis applicable to all these situations, in virtue of the fact that thefouled surface is flushed with liquid. The invention lies primarily inapplying, in these circumstances, an electrical circuit-in causing theliquid as it flushes the fouled surface to become the electrolyte of anelectrolytic cell. The fouled sheet is immersed in the electrolyte;preferably it is an electrode, most, advantageously the cathode, of thecell; but in an case, through electrolysis, water is decomposed, gas isevolved at the metal surface, and gas evolution aids in and renders moreeffective the removal of the fouling material from the metal surface.-Ancillary features of invention are found in the conservation of themetal-treating liquid by washing it from the advancing sheet andreturning it to effectual circulation, and in the unique value ofbrushes of stainless-steel wire, not only for circuit-making contact butalso for efficacy in removing inrolled defilement from the stripsurface.

The cleaning and pickling processes. rendered more effective by the aidof my invention, as herein described, are suitable for the preparationof metallic surfaces generallywhether prior to annealing; afterannealing; after rolling and prior to plating, hot coating, inting,enameling, or other chemical or electro-chemical treatment indeed,wherever a chemically clean surface is desired. In the cold-rolling ofstrip at high speed, lubricant is used to keep the stock cool; but theheat generated in rolling may effect some breaking-down of the lubricantand the heavier products of such breaking-down may be rolled into thesurface of the strip; again, the strip having alread been pickled by aprocess such as those commonly in use, ferric and ferrous salts thesolution is directed back to the pool within the tank. These brushes,rotating as they do in direction opposite to that of strip advance, have.stifiness suillcient to arrest the liquid in its advance. The quantityof water sprayed upon the strip as it approaches these brushes at thedelivery end of the tank is so controlled as to make .good theevaporation and (reduced) drag-out losses, and to maintain the surfaceof the pool within the tank at proper level. This solutionrecoveringsystem is manifestly applicable to chemical and electro-chemicalprocesses generally.

In the cleaning or pickling of some metallic surfaces it may bedesirable to use brushes of other metal than stainless steel. The typeof metallic wire brush to be used will depend upon the speed of striptravel, the nature of the metal being cleaned, etc. For soft stripmetals the brush may be made of a metal softer than stainless steel.

I claim as my invention:

1. The method of continuously cleaning the surface of a moving metalstrip to remove foreign material therefrom, which consists in applyingan aqueous liquid to said strip, tangentially brushing theliquid-carrying surface of said strip with a rotating metallic brushelectrically connected to one terminal of an electric generator, andpassing a current from the other terminal of the generator through saidliquid and brush for rapidly evolving gas electrolytically at thebrushed surface.

2. The method of cleaning the surface of a metal strip to remove foreignmaterial therefrom, which consists in passing an aqueous liquid througha jet-forming electrode connected to one terminal of an electricgenerator, moving the strip past the liquid Jet to impinge the jet onthe surface of said strip, tangentially brushing the jetted surface witha rotating metallic brush electrically connected to the other terminalof said generator, and passing a current through said jet electrode,strip and brush for rapidly evolving gas electrolytically at the surfaceof the strip.

3. The method of continuously cleaning the surface of a moving metalstrip to remove foreign material therefrom, which consists in jetting anaqueous liquid against the surface of said strip, tangentially brushingthe jetted surface with a rotating metallic brush connected to oneterminal of an electric generator, and passing an electric current fromthe strip through the liquid Jet to the other terminal of the generatorfor rapidly evolving gas electrolytically at the Jetted surface of thestrip.

4. The method of continuously cleaning a metal strip, which includespassing the strip over a tank containing cleaning solution, jetting saidcleaning solution against the surface of said strip. tangentiallybrushing the jetted surface with a rotating metallic brush connected atone tenninal of an electric generator, and passing an electric currentfrom the stri through the liquid jet to the other terminal of thegenerator, said current having a current density per square foot of jetcross section area suflicient to produce a rapid electrolytic evolutionof gas at the jetted surface of the strip, all while the strip ispassing over the tank.

5. The method of continuously cleaning the surface of a moving metalstrip to remove foreign material therefrom, which consists in applyingaqueous liquid to said strip, tangentially brushing the liquid-carryingsurface of said strip with a rotating metallic brush electricallyconnected to one terminal of an electric generator, and passing anelectric current from said brush to the strip.

6. In a method of cleaning a moving metallic surface to remove oil,dirt, carbon and oxides, the steps of jetting a continuous stream ofaqueous electrolyte from a jet forming electrode through the atmosphereagainst said moving metallic surface, and passing electric current fromsaid jet forming electrode through said jet of electrolyte to saidmoving metallic surface, said electric current being at sufficientcurrent density to cause rapid evolution of gas by electrolysis at themoving metallic surface in the area of said jet impingement.

JOHN S. NACHTMAN.

